U.S. patent number 5,347,095 [Application Number 08/004,532] was granted by the patent office on 1994-09-13 for electrical receptacle for use with annunciator apparatus for monitoring electrical connections.
Invention is credited to Abraham Zeder.
United States Patent |
5,347,095 |
Zeder |
September 13, 1994 |
Electrical receptacle for use with annunciator apparatus for
monitoring electrical connections
Abstract
An electrical receptacle for use with an annunciator for
indicating the removal of an electrical plug from the electrical
receptacle. The electrical receptacle includes neutral switching
contacts actuated in response to the insertion of a plug into the
receptacle. An input circuit in the annunciator apparatus monitors
the state of the neutral switching contacts and couples signals
produced when a plug is removed to a latching circuit thereby to
produce an audible or electrical indication of plug removal.
Inventors: |
Zeder; Abraham (Andover,
MA) |
Family
ID: |
24916719 |
Appl.
No.: |
08/004,532 |
Filed: |
January 14, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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725979 |
Jul 5, 1991 |
5258744 |
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Current U.S.
Class: |
200/51.09;
200/51.02; 439/188 |
Current CPC
Class: |
G08B
13/1409 (20130101) |
Current International
Class: |
G08B
13/14 (20060101); H01R 033/96 () |
Field of
Search: |
;200/51R,51.02,51.03,51.04,51.09,51.1,51.11,51.12,43.04,43.05
;439/188X,490,489,488,911 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Barrett; Glenn T.
Attorney, Agent or Firm: Pearson & Pearson
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a division of my copending U.S. patent
application Ser. No. 07/725,979 filed Jul. 5, 1991, U.S. Pat. No.
5,258,744, for Annunciator Apparatus for Monitoring Electrical
Connections.
Claims
What is claimed as new and desired to be secured by letters patent
of the United States is:
1. An electrical receptacle for use with an apparatus for detecting
the removal from said receptacle of an electrical plug with a
plurality of male contacts, said apparatus having first and second
signalling inputs, said receptacle being adapted for connection to
power and neutral conductors from a power source and
comprising:
A. receptacle housing means for supporting the electrical plug,
said receptacle housing means having an internal cavity and
apertures defining passages from said internal cavity exteriorly of
said receptacle housing means,
B. a first contact engaging means for engaging one of the male
contacts of the plug, and a second contact engaging means for
engaging another one of the male contacts of the plug, each of said
contact engaging means being supported by said receptacle housing
means in said internal cavity,
C. power terminal wiring means for receiving the power conductor
and neutral terminal wiring means for receiving the neutral
conductor each of said terminal wiring means extending through said
apertures and located partially in said internal cavity and
partially exteriorly to said receptacle housing means and being
adapted for connection to said first signalling input of the
apparatus,
D. power electrical switching means for connecting said power
terminal wiring means to said first contact engaging means and
neutral electrical switching means for connecting said neutral
terminal wiring means to said second contact engaging means, each
of said electrical switching means controlling the conductive state
between said respective terminal wiring means and said contact
engaging means and being positioned in said internal cavity,
E. power switch actuating means and neutral switch actuating means,
each being supported by said receptacle housing means in said
internal cavity and responsive to the insertion of plug male
contacts into said receptacle housing means for changing the
conductive state of said power and neutral electrical switching
means respectively, whereby the conductive state between said first
and second contact engaging means and respective said terminal
means depends on the presence or absence of the plug in said
receptacle housing means.
F. conductive feedthrough means extending from said neutral
switching means and through another of said apertures in said
housing means thereby to provide an electrical connection
exteriorly of said receptacle housing means to said second
signalling input.
2. An electrical receptacle as recited in claim 1 wherein said
receptacle is adapted for supporting a plurality of electrical
plugs, said electrical receptacle including a neutral switching
means for each electrical plug and plurality of said conductive
feedthrough means, each of said conductive feedthrough means being
connected to one of said neutral switching means for providing
independent access to each of said neutral switching means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to annunciator apparatus and more
particularly to apparatus that announces the unauthorized or
inadvertent removal of a plug from an electrical receptacle.
2. Description of Related Art
The removal of an electrical plug from a receptacle is a common
occurrence. In many situations this step occurs as a normal event.
However, in others this step represents an unauthorized or
inadvertent action that requires some immediate response. For
example, removing the plug of an electrical appliance in a store
may indicate that someone is stealing the appliance. In other
situations the removal of the plug may indicate that critical
apparatus has ceased to function. In these or other situations it
is important to announce the occurrence of such a step by audible
or electrical signalling.
These situations, particularly attempted thefts of electrical
equipment, have led to the development of various theft deterring
apparatus. The simplest apparatus for deterring theft comprises
mechanical locking assemblies, such as cables and locks, that
physically bind an appliance to a wall, counter or other fixture to
prevent its physical removal. Such mechanical assemblies, however,
can be cumbersome to use, especially in stores where individuals
properly may move the appliances. It is relatively easy for an
individual intent on stealing the appliance to defeat these
mechanical locking assemblies and remove the appliance. Moreover,
these assemblies do not inherently have any capability to announce
the occurrence of unauthorized actions.
There is a range of alarms and other annunciator apparatus that
provides on-site or remote signalling that are used in a theft
deterring role. In one approach electrical receptacles are modified
to provide mechanical or optical switching functions that respond
to the presence or absence of a ground or neutral plug terminal or
the like. Alarm circuits provide an alarm whenever a plug is not
present. The following United States Letters Patent disclose
various embodiments of such apparatus:
______________________________________ 3,090,948 (1963) Cremer
3,192,518 (1965) Sliman 4,097,843 (1978) Basile 4,591,732 (1986)
Neuenschwander 4,845,719 (1989) Posey
______________________________________
In accordance with other approaches separate electronic monitoring
units mount on appliances or centrally disposed electronic circuits
monitor wire lengths or other conditions that could indicate the
removal of an electrical plug. The following United States Letters
Patent disclose apparatus of this general category:
______________________________________ 4,327,360 (1982) Brown
4,680,574 (1987) Ruffner 4,736,195 (1988) McMurtry et al 4,945,335
(1990) Kimura et al ______________________________________
The following United States Letters patent disclose apparatus that
monitors the insertion or removal of a plug from a receptacle:
______________________________________ 4,075,617 (1978) Wireman
4,028,691 (1977) Zeder ______________________________________
The Wireman patent discloses a structure including modified poles
in an electrical receptacle. Specifically each receptacle contains
an added spring coil between a neutral connection and an auxiliary
contact. The auxiliary contact has insulating portions on either
side of a conductive portion. Each insulating portion isolates the
neutral and auxiliary connections when a plug is either in place or
removed. A momentary contact occurs as a plug is inserted or
removed. Alarm circuitry associated with the receptacle responds to
both transient conditions by sounding an alarm. An operator must
shift the system to a test mode to disable the alarm circuit before
inserting a plug. If the system is not in a test mode, plug
insertion will produce an alarm. Thus, this apparatus may produce
false indications of problems unless specific operating steps are
followed.
In accordance with the Zeder patent, filed by the same Applicant as
the present invention, a plunger extends through the center of each
receptacle of a duplex outlet. Each plunger controls corresponding
external switching contacts that constitute an input to an alarm
circuit. Any time a plug is removed, spring bias on the
corresponding switch contacts opens the switch and an alarm sounds.
A special cover can be located in any unused pole position to
prevent erroneous alarms, but such covers are subject to being
lost. The plunger can be broken; when this occurs, the entire
receptacle must be replaced. It is also possible to block the
plunger while the plug is installed and then remove the plug
without any alarm. Despite these characteristics, apparatus
constructed in accordance with the Zeder patent has been accepted
for a number of applications where theft deterrence and other
monitoring are important.
SUMMARY
Therefore it is an object of this invention to provide apparatus
that reliably announces the unauthorized or unintentional removal
of a plug from a receptacle.
Another object of this invention is to provide an apparatus for
announcing the removal of a plug from a receptacle that
distinguishes between the steps of plug removal and plug
insertion.
Still another object of this invention is to provide annunciator
apparatus that is reliable and simple to operate.
Annunciator apparatus constructed in accordance with this invention
monitors the transition of an electrical switch in an electrical
circuit from a first state to a second state. The annunciator
apparatus includes a power supply means that connects to the
electrical circuit for energizing the apparatus. An input circuit
produces first and second transition signals in response to switch
transitions from the first to the second state and from the second
to the first state respectively. Transition sensing produces
transition sensed signals in response to the first transition
signals. Annunciators respond to the transition sensed signal by
producing an alarm.
More specifically, this invention is particularly adapted for use
with electrical receptacles that include a switching actuator that
makes electrical contact between external terminals and internal
contact structures. The input circuit connects to the electrical
switch and produces the first transition signal in response to the
plug's being removed from the receptacle and a second transition
signal in response to the plug's being inserted into the
receptacle. The transition sensing means produce a transition
sensed signal in response to the first transition signal to cause
the annunciator to produce an audible or electrical indication. The
electrical switch is constituted by switching contacts on the
neutral side of the receptacle.
BRIEF DESCRIPTION OF THE DRAWINGS
The appended claims particularly point out and distinctly claim the
subject matter of this invention. The various objects, advantages
and novel features of this invention will be more fully apparent
from a reading of the following detailed description in conjunction
with the accompanying drawings in which like reference numerals
refer to like parts, and in which:
FIG. 1 is a perspective view of an embodiment of an annunciator
apparatus that embodies this invention;
FIG. 2 is an exploded perspective view of the components of one
embodiment of an electrical receptacle adapted to be used with this
invention;
FIG. 3 is an exploded perspective view of another embodiment of an
electrical receptacle adapted to be utilized in this invention;
and
FIG. 4 is a schematic view of the apparatus circuitry utilized in
accordance with this invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
FIG. 1 discloses one embodiment of annunciator apparatus 10
constructed in accordance with this invention with a housing 11 and
a power cord 12 that connects to a standard 120- or 240-volt AC
supply with power and neutral conductors and normally a ground
conductor. Typically the power cord connects to a receptacle in a
secure location remote from the apparatus being monitored.
The specific apparatus 10 in FIG. 1 has four receptacle positions
13, 14, 15 and 16 and depicts a single plug 17 inserted in
receptacle position 13. Normally the receptacle positions 13 and 14
and associated structure are combined in a single duplex outlet.
Similarly another duplex outlet can define the receptacle positions
15 and 16. In the following discussion the term "receptacle" means
to include the structure associated with a "receptacle position".
Detailed receptacle structures are discussed in more detail later
in connection with FIGS. 2 and 3.
An indicator light 20 illuminates whenever ac power energizes the
receptacles 13 through 17. An alarm light 21 illuminates as a
visual indictor that the alarm circuitry is working. An audio alarm
sounds from a speaker 22, and a relay jack 23 provides a means for
indicating an alarm to a remote location is connected to normally
open or normally closed relay contacts inside the housing 11. A
key-operated reset switch 24 provides a means for authorized
personnel to clear the various alarm indications after an alarm
condition; the alarm light 21 extinguishes whenever the reset
switch 24 is active. The housing 10 additionally includes a
plurality of input jacks 25, 26, 27 and 28 that adapt the apparatus
for monitoring remote locations in response to external switch
contacts. A circuit breaker reset button 29 allows personnel to
reset an internal circuit breaker that provides overload
protection.
If the apparatus 10 is operating in the configuration shown in FIG.
1, both the power indicator 20 and the alarm light 21 are lit. An
authorized removal of the plug 17 requires personnel to operate the
key-operated reset switch 24 to block any alarm by disabling the
alarm circuit. When this occurs, the alarm light 21 turns off. Then
the individual returns the reset switch 24 to a normal position and
enables the alarm circuit and the alarm light 21 turns on again. If
someone removes the plug without authorization, the apparatus 10
announces the action. Specifically, the speaker 22 produces an
audible alarm and the relay contacts associated with the relay jack
23 change state. This alarm annunciation continues until authorized
personnel activate the reset switch 24. If someone inserts a plug
into the receptacle 14, 15 or 16, no alarm occurs. No alarms occur
as a result of the absence of any plug in any receptacle position.
Only the removal of a plug without authorization produces an
alarm.
FIG. 2 discloses one embodiment of a standard duplex outlet 30 that
is modified in accordance with this invention. For purposes of
explanation it is assumed that the duplex outlet 30 corresponds to
the duplex outlet that provides receptacle positions 13 and 14 in
FIG. 1. The outlet 30 includes an insulating base 31 and a
complementary insulating cover 32 that form a receptacle having
diverse barriers and internal cavities for accepting and supporting
the various conductive and other internal components of the
receptacle. A ground strap 33 with a central rivet 34 that passes
through apertures in the housing 31 and cover 32 clamps the various
parts together. A neutral wiring terminal 35 and power wiring
terminal 36 in parallel side cavities of the housing 31 provide a
means for affixing power and neutral ac supply conductors to the
duplex outlet 30. Insulating spacers 37 provide an insulating
barrier if it is desired to separate the two poles by severing
links on the terminals 35 and 36.
U-shaped power contact engaging structures 40 with spaced female
contacts 41 and a tab 42 on opposite legs of the U-shaped structure
lie in other cavities of the housing 31. Neutral contact engaging
structures 43 have a similar structure with female contacts 44 and
tabs 45. In accordance with this invention, however, the neutral
contact engaging structures 43 are modified by adding downward
extensions 46 from the tab 45. Each extension 46 passes through and
exits externally to the base 31 and thereby constitutes a
conductive feedthrough means.
The cover 32 has an internal barrier and slot, such as the barrier
47 and slot 50 shown with respect to the receptacle 14 that
receives an activating disk 51. Activating disks 51 are associated
with each of the power and neutral contact structures and normally
align to the center of the switch with respect to tabs 42 and 45
respectively. When the duplex outlet 30 is assembled, the
activating disks 51 also align under the power and neutral slots or
apertures 52 and 53 formed at each of the receptacle positions.
As the male terminals of a plug pass through the slots 52 and 53
they force the corresponding activating disks 51 simultaneously
toward the sides of the outlet 30. The activating disks 51 engage
and displace the tabs 42 and 45 simultaneously. The tabs 45 contact
tabs 54 to connect the neutral terminal 35 and the neutral contact
structures 43. A similar action brings the tabs 42 into contact
with the tabs 55 on the power wiring terminal 36. When a plug is
removed from the receptacle, the tabs 42 and 45 return to an
unbiased state and separate from the tabs 55 and 54 thereby
breaking any electrical contact between them. The tabs 42 and 55
and the tabs 45 and 54 constitute electrical switches with first
and second switching terminals. In this embodiment the disks 51 act
as switch actuators that respond to the insertion of plug contacts
into the receptacle.
FIG. 3 discloses another embodiment of a standard duplex outlet 60
that is modified for use with this invention. It is assumed that
the duplex receptacle 60 corresponds to the duplex outlet that
provides receptacle positions 15 and 16. The outlet 60 comprises an
insulating base 61 and an insulating cover 62. A ground strap 63
with a rivet 64 clamps the various parts of the outlet 60 in an
assembly. A neutral wiring terminal 65 and a power wiring terminal
66 lie in cavities adjacent opposite sides of the housing 61.
Power contact structures 70 and neutral contact structures 71 lie
in internal cavities adjacent the power and neutral wiring
terminals 66 and 65. Each contact structure generally has a square
base 72 with one elongated side 73 that generally extends beyond
the square. Three upstanding legs 74 with flared upper portions
form a universal female contact that accepts different plug contact
configurations. The cover 62 with its straight slots, such as slots
52 and 53, defines which of the pairs of female contacts 74 will
engage the plug contacts. An extension 75 from the elongated side
73 on each of the power and neutral contact structures 70 and 71
extends toward the cover 62. In accordance with this invention the
neutral contact structures 71 have extensions 76 that exit the
housing 61.
Transverse slots 77 formed in the base 61 serve as tracks for
L-shaped activators 80. Each activator has a leg 81 that rides on
one of the tracks. An extension 82 at right angles to the leg 81 is
offset from the end to align with one of the female contacts and to
block access to the slots 52 and 53. A remote end of each leg 81
abuts one of the extensions 75 that normally is spaced from a
contact 83 on a corresponding one of the neutral and power
terminals 65 and 66.
When the male terminals of a plug enter through the slots 52 and
53, they engage corresponding extensions 82 and force them together
so the end portions displace the extensions 75 into the respective
contacts 83. When the plug is removed, the extensions 75 return to
an unbiased condition and break the contacts between the terminals
65 and 66 and the corresponding contact structures 71 and 70.
Thus, FIGS. 2 and 3 disclose diverse embodiments of electrical
outlets with receptacles modified in accordance with this
invention. The base 31 and cover 32 in FIG. 2 and the base 61 and
cover 62 in FIG. 3 support electrical plugs. Each receptacle
contains neutral and power wiring terminal means in the form of the
terminals 35 and 36 and 65 and 66. Each receptacle contains contact
means for engaging the male contacts on a plug in the form of the
female contact structures 41 and 44 in FIG. 2 and contact
structures 74 in FIG. 3. Each receptacle contains an electrical
switch in a form of the tabs 45 and 54 in FIG. 2 and the extensions
75 and contacts 83 in FIG. 3 that shift between a first, or closed
state when a plug is inserted to a second, or open, position when
the plug is removed. The activating disks 51 and the activators 80
in FIGS. 2 and 3 respectively constitute a switch actuating means
that responds to the insertion of the plug contacts into the
receptacle for closing the electrical switching means, The
extensions 46 and 76 in FIGS. 2 and 3 constitute conductive means
connected to the neutral switching means that extend through the
receptacle means.
The schematic of FIG. 4 illustrates one embodiment of an alarm or
annunciator circuit for installation in the housing 11 of FIG. 1
and for operation with receptacles such as shown in FIGS. 2 and 3
or any other electrical device that uses a switch to identify
particular events. In general terms, the annunciator circuit of
FIG. 4 includes a power supply circuit 100 that connects to an AC
supply for producing various power supply voltages for the
annunciator circuit. An input circuit 101 monitors the various
switching contacts to produce first and second transition signals.
In accordance with this embodiment, the input circuit 101 produces
a first transition signal when a plug is removed from a receptacle
and a second transition signal when the plug is inserted. A
transition signal circuit 102 monitors the input circuit 101 and
responds to a first transition signal by generating a transition
sensed signal that activates the various annunciator elements in an
indicator circuit 103.
The power supply circuit 100 includes a plug 104 that connects a
power conductor 104p, a neutral conductor 104n and ground conductor
104g to an external AC power source. The AC power indicator 20 in
FIG. 1 comprises a neon lamp 20 connected across the power and
neutral conductors 104p and 104n on the load side of a circuit
breaker 29a that includes the reset button 29 shown in FIG. 1.
Varistors (VAR) or other spike suppression elements connect between
the various conductors.
The conductors 104p and 104n and 104g connect to the various
receptacles in the outlets 30 and 60. FIG. 4 depicts schematically
the receptacle 30 with its power contact structures 40 and neutral
contact structures 43. Spaced arrows 45 and 54 represent the
normally open switching position of tabs 45 and 54 and a conductor
46 represents the extension 46. Likewise FIG. 4 schematically
depicts the receptacle 60 with its power and neutral contact
structures 70 and 71, the extensions 75, the contacts 83 on the
neutral wiring terminal 66 and the conductor 76 that represents the
extension 76 from the neutral contact structure 71. So long as the
plug 104 is plugged into a powered electrical outlet and the
circuit breaker 29a is closed, the lamp 20 is on and the outlets 30
and 60 are energized when a plug is inserted into the outlets 30
and 60. The circuit breaker 29a provides overload protection for
the appliances or other electrical devices that plug into the
outlets 30 and 60.
The power supply 100 also includes a transformer 105 with a primary
105P connected to the power and neutral conductors 104p and 104n. A
secondary 105S connects to the ground conductor 104g and to a
rectifier circuit comprising a diode 106 and a filter capacitor 107
that provides a filtered DC output voltage. The normally closed
reset switch 24 couples this DC output voltage onto a DC bus
108.
A rechargeable battery circuit including battery 110, a charge
limiting resistor 111 and a blocking diode 112 enable the alarm
functions in the circuit to operate even if the plug 104
temporarily disconnects from the remote power supply 100. While an
AC voltage energizes the transformer primary 105P, the rectifier
circuit provides a trickle charge to the battery 110 through the
resistor 111. When the AC voltage is removed, the battery 110
discharges through the diode 112 to provide power to the remainder
of the circuit.
The input circuit 101 has a number of analogous circuit legs for
each of the receptacles 13 through 16. In a first leg a resistor
113 connects between the DC bus 108 at a junction A of the
extensions 46 from the receptacle 14 and a capacitor 114. A
resistor 115 connects to ground and to a junction formed by the
other side of the capacitor 114 and the anode terminal of a diode
116. The capacitor 114 and resistor 115 constitute a high pass
filter that produces first and second transition signals in
response to each shift in state of the neutral terminal switching
means constituted in the receptacle 30 by the tabs 45 and 54. When
a plug is inserted in a receptacle 14, the tabs 45 and 54 are in
contact, so the junction A is maintained at a ground potential.
When the plug is removed, the tabs 45 and 54 separate, so the
potential at junction A shifts to the voltage on the DC bus 108.
The high-pass filter circuit comprising the capacitor 114 and 115
converts this transition into a positive going pulse at the anode
terminal 116a of the diode 116. This pulse then passes through the
diode 116 to the resistor 117 and a resistor 118 in the transition
signal circuit 102.
When a plug is inserted, the voltage at junction shifts to ground,
and the filter circuit comprising the capacitor 114 and 115
converts this transition into a negative going pulse. However, the
diode 116 blocks this pulse from reaching the resistor 117 and 118.
Thus, the diode 116 is an example of a unidirectional conducting
means in series between the high pass filter means and the
transition signal circuit that couples only the first transition
signals constituted by positive pulses to the transition signal
circuit 102.
A second input leg of the input circuit 101 comprises a resistor
120 between the DC bus 108 and a capacitor 121, the junction of the
resistor 120 and 121 being connected to the extension 46 from the
receptacle 13. The capacitor 121 and another resistor 122, that
connects to ground, form another high pass filter that connects to
a diode 123. Similar input legs 124 and 125 connect to monitor the
switching contacts in each of the receptacles 16 and 15 associated
with the duplex outlet 60.
FIG. 4 additionally shows two analogous input legs 126 and 127 for
monitoring the input jacks 27 and 28 of FIG. 1. If such jacks
connect to remote switches with grounded contacts, the input
resistors and high pass filters in each of legs 126 and 127 provide
first and second transition signals that monitor those remote
switching contacts.
All the diode cathodes, such as the cathode 116c, connect in common
to provide a logical OR input to the transition circuit 102,
particularly an input voltage divider comprising the resistor 117
and resistor 118. A capacitor 130 in parallel with the resistor 118
bypasses certain noise signals that may appear in the circuit to
the ground conductor 104g thereby minimizing false input signals
and alarms in response to such noise signals.
Whenever a plug is removed, the leading edge of the resulting
positive-going pulse through the resistors 117 and 118 in the
transition signal circuit 102 produces an input signal for a
bipolar latching means in the form of a D-type latch 133. The
clocking (CL) input connects to the junction of the resistors 117
and 118; the data (D) input, to the DC bus 108 through a coupling
resistor; and the overriding set (S) input to ground. As known,
with the D input held at a high potential, a positive-going signal
transition at the CL input sets the latch 133. When the latch 133
is set, the Q output is at a positive, or TRUE, level and the Q
output is at a ground, or FALSE, level.
The transition signal circuit 102 additionally includes an
initializing circuit in the form of a capacitor 135 between the DC
power bus 108 and the overriding reset (R) input of the latch 133.
When power is first applied to the power supply circuit 100,
initial transients could cause a false clocking signal to be
applied to the latch 133 without the capacitor 135. During this
interval, however, the capacitor 135 maintains an active input at
the overriding reset (R) input of the latch 133, so it can not set
for an initial startup interval. These transients cease and stable
operating conditions exist before the capacitor 135 charges the
input signal to the overriding reset (R) input shifts to enable the
latch 133 to respond to clocking inputs.
Any time a set of contacts being monitored by the input circuit 101
shifts from a closed to an open condition, the latch 133 sets and
remains set until authorized personnel activate the reset switch
24. When this occurs, the normally closed contacts of the switch 24
open and interrupt the power on the DC bus 108 thereby to disable
the alarm circuit. This condition remains until the reset key
operated switch 24 returns to its operating condition (i.e., to
close the contacts) whereupon power is again applied to the DC bus
108 to enable the alarm circuit latch 133 to respond to a clocking
signal.
The specific indicating circuit 103 in FIG. 4 provides audible and
electrical indications whenever an alarm condition exists. When a
plug is removed and the latch 133 sets, a switching circuit,
including a switching transistor 143, closes and establishes a
return path for an audio generator, represented by the speaker 22,
to produce an audible signal.
As shown in FIG. 4 normally opened contacts in the relay 23 provide
an electrical annunciation. In this particular embodiment another
switching circuit including a switching transistor 144 connects to
the Q output of the latch 133 to energize the relay 23 and close
the contacts during normal operations. When the latch 133 sets, the
switching transistor 144 stops conducting, so the relay contacts
open until the latch 133 resets. Thus continuity through the relay
jack 23 in FIG. 1 indicates proper operation while a discontinuity
indicates an abnormal condition.
In many applications external devices can produce significant noise
signals on the power line between the neutral conductor 104n and
the ground conductor 104g. The circuitry in FIG. 4 is immune to
such noise signals. The input circuit 101 inherently blocks any
noise signals that drive the neutral conductor 104n negative with
respect to the ground conductor 104g. A diode 145 provides noise
immunity with respect to any signals that drive the neutral
conductor 104n positive with respect to the ground conductor 104g.
Noise signals of positive polarity exist could filter through the
receptacles 13 through 16 and the input circuit 101 and appear as
positive-going transitions at the CL input of the latch 133 thereby
generating false alarm annunciations. However, the diode 145, with
its anode connected to the neutral conductor 104n and its cathode
connected to the reset (R) input of the latch 133, couples such
positive noise signals in parallel to the reset (R) input. Given
the relative time delays through the input circuit 101, positive
polarity noise signals produce an overriding resetting action at
the latch 133 before the noise driven transition signals arrive at
the CL input. Thus, the diode 145 provides immunity with respect to
noise signals of a positive polarity by disabling the operation of
the latch 133 for the duration of the noise signals.
Therefore in accordance with this invention annunciation apparatus,
such as shown in FIG. 1 that includes receptacles modified as shown
in FIGS. 2 and 3 and circuitry of the type shown in FIG. 4,
overcomes the deficiencies of the prior art. The apparatus
distinguishes between plug insertion and removal and produces an
alarm only when a plug is removed. If a receptacle is empty or if a
plug is inserted, there is no alarm. The circuitry used in the
apparatus constructed in accordance with this invention is readily
and reliably implemented by persons of ordinary skill in the art.
Consequently, annunciation apparatus that embodies this invention
is reliable, simple to operate and economical to produce.
This invention has been disclosed in terms of certain embodiments.
It will be apparent that many modifications can be made to the
disclosed apparatus without departing from the invention. For
example, the specific apparatus shown in FIG. 1 contains two duplex
outlets. This invention is also adapted for implementation with
single receptacle outlets or multiple outlets and with or without
remote switch input jacks. The circuitry of FIG. 4 can readily
accommodate any reasonable number of switches by adding or deleting
input legs in the input circuit 101. The apparatus is shown with
specific embodiments of audible and electrical outputs. Other
combinations can be included as can other specific alarms. Various
modifications can be made to the annunciation circuit of FIG. 4.
Different bipolar latching circuits can replace the D-type latch
133. Alternative output signal driver circuits can be added or
substituted for the specifically disclosed switching transistor
circuits. Different input circuit configurations are also possible.
All of these modifications and variations may be made while still
achieving some or all of the objectives of this invention.
Therefore, it is the intent of the appended claims to cover all
such variations and modifications as come within the true spirit
and scope of this invention.
* * * * *